Prince William and Prince Harry have continued their late mother's efforts to destigmatize mental health issues in recent years. And now, for the first time, Will is addressing Princess Diana's own struggles with low self-esteem and an eating disorder.

In a new documentary from British broadcaster Channel Four entitled Wasting Away: The Truth About Anorexia, William discusses the importance of speaking openly about eating disorders and other issues of mental health with Mark Austin, a former anchor for a British news network, and Austin's daughter Maddy, who is battling anorexia. According to British Vogue, Will acknowledged the Austin family's bravery for opening up about Maddy's struggles.

"We need to normalize the conversation about mental health," he said. "The fact that you are speaking out is incredibly brave."

Being open about struggling with an eating disorder helps others feel less alone.

In a bombshell 1995 interview, Diana told the BBC's Martin Bashir how her tumultuous marriage to and divorce from Prince Charles had affected her self-confidence and mental health. "I didn't like myself, I was ashamed because I couldn't cope with the pressures," Lady Di said. "I had bulimia for a number of years, and that's like a secret disease...It's a repetitive pattern which is very destructive to yourself." She continued, "It was a symptom of what was going on in my marriage. I was crying out for help, but giving the wrong signals, and people were using my bulimia as a coat on a hanger: They decided that was the problem — Diana was unstable."

As the National Eating Disorders Association (NEDA) explains, about 1 percent of young women and about 0.1 percent of young men meet the criteria for bulimia at any given time. Additionally, people with eating disorders often also have other mental health issues, such as anxiety or depression, which can even more significantly affect their relationships with their body and food. However, as the Mayo Clinic explains, those struggling with these disorders often do so in secret because they are often accompanied by feelings of shame—and because those who suffer from bulimia don't necessarily look "unhealthy"—which makes it all the more important when those who are able to speak up about their experiences.

When asked by Austin whether he's proud of his mother for speaking out about her struggles, William said, "Absolutely. These are illnesses. Mental health needs to be taken as seriously as physical health."

Speaking honestly about mental illness is the first step in breaking stigma.

To that end, Prince William, Princess Kate, and Prince Harry started the Heads Together campaign in 2016 to bolster other charities' efforts in "tackling stigma, raising awareness, and providing vital help for people with mental health challenges," according to the campaign's website. Since then, the three have spoken openly about issues of mental health. Most recently, Harry was featured on the Telegraph's Mad World podcast, where he revealed his own struggles with depression following his mother's 1997 death.

"I can safely say that losing my mum at the age of 12 and, therefore, shutting down all of my emotions for the last 20 years has had a quite serious effect on not only my personal life but my work as well," he said. "I have probably been very close to a complete breakdown on numerous occasions when all sorts of grief and sort of lies and misconceptions and everything are coming to you from every angle."

Harry also revealed that William encouraged him to seek therapy. And, since doing so, he has been in a much better place. "Because of the process I have been through over the past two and a half years, I've now been able to take my work [and private life] seriously," he said, "and [I've] been able to put blood, sweat, and tears into the things that really make a difference—and things that I think will make a difference to everybody else."